This invention relates to a tension providing device which provide a fixed tension. More particularly, this invention relates to a tension providing device by pressing a chain or a timing belt which drives a cam shaft of an engine of 2 wheel automobile or 4 wheel automobile.
A tension providing device is generally used as a chain tensioner or a belt tensioner.
This operation is carried out so as to press the chain or the belt in a fixed direction when the chain or the belt extends or slackens or even if a distance between pulleys changes. By this, the chain or the belt is provided a fixed tension.
A conventional tension providing device used for this purpose will be described in details referring to FIG. 6 and FIG. 7.
This tension providing device is developed by the same inventor of this invention.
The material portions of this invention are composed of:
A casing 1 having a cavity portion 1a in an axial direction.
A rotary shaft 2 inserted pivotally in a base portion side (right end portion) of the casing 1.
A pressing body 3 screwed with the top end portion of this rotary shaft.
A torsion spring which is inserted in the rotary shaft outwardly and provides a rotary force to the rotary shaft, one end 4a of said torsion spring being inserted in a latching groove 2a the rotary shaft and another end 4b being inserted into a long groove 1b at the top end of the casing, and
a seal bolt 6 screwed with a base end portion of the casing 1 through an O-ring.
In the casing 1 a flange portion 1g having an attached hole 1f is formed at the periphery of the top end side of a cylinder having a cavity portion. This device is attached to an objective device by the insertion of a bolt at the attaching hole thereof.
At the top end portion of the pushing body 40, a cap 8 is pimed with a spring pin 7. The cup 8 presses a chain or a belt so as to maintain a fixed tension. The pushing body 3 is formed nearly an oval in the periphery thereof. And restrained so that it may not rotates when it is inserted in a bearing a formed to be a same shape sliding hole as the periphery of the pushing body. Accordingly, the rotary movement of the rotary shaft 2 is changed to the sliding movement of the pushing body 3 in the axial direction, whereby the pushing body 3 is adapted to advance to the outside the casing.
Protruding pieces 9a are provided at the trisected portions of the outer circumference of the bearing 9 respectively, said each protruding piece 9a being screwed with a dent portion 1e provided at the inner circumference of the top end portion of the casing 1 to prevent the rotation. Further, a cir-clip is inserted in a ring groove provided at the inner circumference of the top end portion of the casing from outside the bearing 9 to prevent the removing.
The rotation of the rotary shaft 2 is carried out by the torsion spring secured to the outside the shaft 2. This torsion spring 4 is previously wound to provide a fixed torque, thereby rotating the rotary shaft with the aid of stability force.
In drawings, the numeral 10 is a stopper, said stopper latching the top end thereof to a latching groove 2a of the rotary shaft and the base end portion thereof to the stopper groove IC respectively to lock the rotation of the rotary shaft.
Such tension providing device locks the rotation of the shaft 2 with stopper 10 in a state that said torsion spring is wound and is fixedly attached to an outer wall of a machine such as engine or the like with bolts in a locking state. In use, the stopper is separately removed from the casing 1 and the bolt 6 is screwed with base end portion of the casing 1 to seal. By this base end portion of the casing 1 to seal. By this removing of the stopper 10, the rotary shaft 2 rotates with the aid of the stability of the torsion spring 4, thereby advancing the pushing body 3. This rotation further pushes the chain or the belt to act so as to provide a fixed tension.
However, this conventional device has the following defects.
In the conventional device, since the base end side of the casing 1 is sealed with O-ring and seal bolt, the seal is very good. However, the top end portion of the casing inserted therein is inferior to the seal. In other words, since a B portion of a long groove 1b wherein another end 4b of the torsion spring 4 is inserted, a C portion where a pushing body 3 contacts with a bearing 9, a D portion where the bearing 9 internally contacts with casing 1, a E portion where the pushing body 3 contacts with cap 8, a F portion which is an axis of spring pin 7 which pins the cap 8, and a G portion where the spring pin 7 contacts with cap 8 are not subjected any sealing treatment, these portions are inferior to the seal.
Accordingly, when these device is used as it is, said device occurs corrosion in each member or mixing of foreign matters such as dust and the like due to the inner environment, thereby causing a problem to decrease the normal operation of said device. In order to maintain the normal operation of the device, the coating of lubricant to each member and the filling the lubricant in the casing are performed. However, the seal is still incomplete and a fundamental solution such as leakage of said lubricant to the outside.
The leakage of said lubricant oil presents a specially important problem when the conventional device is used as a belt tensioner. When the conventional device is used as a chain tensioner, its chain is usually suspended in an environment surrounded by oil such as in a tank or the like. Accordingly, since the conventional device is used in a state having no lubricant or a state causing no trouble even if the lubricant leaks, such leakage presents no real problem. However, when the conventional device is used as a belt tensioner, since it is suspended in air outside an engine case in like manner to a timing belt, it is used in a state filled with lubricant oil. Accordingly, if the lubricant oil leaks, the lubricant oil may not only stick to the belt, but also obstruct its operation and deteriorate the belt itself. Accordingly, if the conventional tension providing device is used as a belt tensioner, the leakage problem of said lubricant oil must be solved.